This invention relates to transmissions, to infinitely variable speed transmissions, and to belt transmissions well suited for vehicular use, among other applications. More specifically, the invention deals with improvements in or relating to variable diameter pulley systems included in belt transmissions, particularly to the driven pulley and hydraulic circuit means associated therewith.
Belt transmissions have been known and used extensively on motor vehicles. They include a variable diameter pulley system comprising a drive pulley on a transmission main shaft (primary shaft) and a driven pulley on a countershaft (secondary shaft), with a V-belt extending around the two pulleys. Each V-groove pulley is divided into a pair of halves known as pulley cones. One of the pulley cones is axially displaceable towards and away from the other in order to controllably vary the effective diameter of the pulley. Hydraulic fluid pressure is usually employed for controlling the axial position of the movable pulley cone with respect to the fixed pulley cone.
Difficulties have been encountered in controlling the axial position of the movable cone of the driven pulley, in particular, as its speed of rotation becomes very high with upshifting. The hydraulic mainline fluid fed into the actuating fluid chamber of the driven pulley movable cone develops a centrifugal force such that its axial component tends to displace the movable cone in the direction opposite to the desired direction of cone movement for upshifting. It has therefore been suggested to provide a counterbalance chamber opposite the actuation chamber. This counterbalance chamber is supplied as required, with fluid under pressure, so that the centrifugal force of the fluid in the actuation chamber may be counterbalanced by that of the fluid in the counterbalance chamber.
Japanese Laid Open Patent Application No. 57-171154 represents an example of such known counterbalancing means. This prior application teaches to direct the outflow of hydraulic fluid from a torque converter into the counterbalance chamber. An objection to this scheme is that it is applicable only to transmissions of the class incorporating a hydraulic torque converter. Additionally, the outflow from the torque converter cannot possibly be passed through a fluid cooler prior to introduction into the counterbalance chamber.
Japanese Laid Open Patent Application No. 60-104848 teaches to form a counterbalance chamber providing a tubular member which concentrically surrounds the countershaft and the counterbalance chamber is slidably held against the back of a member defining the actuation chamber. This prior art device has the weakness that the area occurring centrifugal force in the counterbalance chamber is always of the smaller size than the area of the actuation chamber and so may therefore fail to develop a sufficient counterbalancing force.
Needless to say, the counterbalance chamber must be of sufficient capacity to enable the fluid therein to counteract the centrifugal force of the fluid in the actuation chamber. No less important, however, is the fact that the hydraulic fluid be infallibly fed into the counterbalance chamber whenever the need arises for cancelling the centrifugal force of the fluid in the actuation chamber. It is undesirable that, as in the second recited prior art device, part of the mainline fluid be directed into the counterbalance chamber, in view of consequent changes in the mainline pressure fed to other parts of the transmission. The counterbalance chamber should be fed from some source of fluid pressure different from the source of mainline pressure.
Belt transmissions of the type in question have had another problem that, as far as the applicant is aware, has been left unsolved Generally, in such belt transmissions, the countershaft with the driven pulley thereon is disposed considerably above the level of the transmission main shaft having the drive pulley mounted thereon, because of design requirements such as the large pulley diameters for a wide range of speed ratios obtainable and the compact arrangement of the parts within a minimum size housing Further, the countershaft is geared to a transmission output shaft because of the need for reducing the speed of rotation of the countershaft.
Conventionally, the countershaft as well as the reduction gearing has been lubricated by oil splashed by the final drive gear meshing with a pinion on the transmission output shaft. However, these moving parts have inevitably been poorly lubricated when the vehicle is traveling at low speed because then the speed of rotation of the final drive gear is also low.